High-torque resorbable screws

ABSTRACT

A high-torque fastener having a threaded shaft and a star-shaped head is disclosed. The high-torque fastener is made of a resorbable or other non-magnetic material. A mating driver snugly fits around the star-shaped head of the fastener, to thereby apply torque to the perimeter of the star-shaped head. The driver can be made disposable, and the driver and fastener packaged together in a single, disposable assembly. Additionally, the driver can be color coded to indicate the size of the fastener which is pre-attached to the driver in the packaging.

PRIORITY INFORMATION

This application is a continuation of Ser. No. 09/888,786 filed Jun. 25,2001, now U.S. Pat. No. 6,343,531, which is a continuation of Ser. No.09/555,344 filed May 22, 2000, now U.S. Pat. No. 6,269,716, which claimsthe benefit of U.S. Provisional Application No. 60/066,237, filed onNov. 20, 1997 and entitled CORRUGATED DRIVE SCREW AND MATING DRIVER, thecontents of which are expressly incorporated herein by reference.

RELATED APPLICATION INFORMATION

This application is related to co-pending U.S. application Ser. No.08/699,673, filed on Aug. 19, 1996 and entitled RESORBABLE,MACRO-POROUS, NON-COLLAPSING AND FLEXIBLE MEMBRANE BARRIER FOR SKELETALREPAIR AND REGENERATION, which is commonly assigned and the contents ofwhich are expressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to fixation devices and, moreparticularly, to biologically compatible screws and matching drivers.

2. Description of Related Art

Since the beginning of recorded history, mankind has exhibited aninsatiable appetite for constructing new devices and repairing brokenones. One meter for measuring the progress of a society through thegenerations has been the creativeness and craftsmanship of thatsocieties' architects and engineers.

From ancient wooden aqueducts of the Nile, to lightweight compositionalstructures of the Space Shuttle, to sophisticated artificial joints ofmodern medicine, a common ingredient has always been the fastener.Whether the fastener is threaded, removable, or integral with thestructure, an accepted engineering principle is that the strength of aproduct is only as great as the product's weakest link.

In the interest of promoting strength above all else, the prior art hasprimarily endeavored to construct metallic fasteners of varying sizesand shapes for the majority of applications. The strength of the metalfastener, however, is not achieved without costs. For many applications,metal can be relatively heavy, expensive, and subject to corrosion.Metal fasteners generally are not recyclable and, additionally, areneither biocompatible nor resorbable, when used in connection withmedical applications.

Threaded, resorbable fasteners have existed in the prior art for medicalapplications, such as bone repair and regeneration. A typical resorbablefastener comprises a threaded shaft, a head, and an internal socketdisposed within the head for accommodating a driver therein. Thisinternal-socket fastener, although biocompatible and resorbable, hassuffered from design deficiencies.

Since the prior art resorbable fastener is designed to be secured tobone within the human body, tissue or other debris may be introducedinto the internal socket of the fastener. Materials introduced into theinternal socket of the fastener can substantially attenuate or eliminateproper operability of the fastener. For example, a surgeon may havedifficulty properly fitting a driver into the internal socket of afastener that has become partially occluded with debris or human tissue.Since resorbable fasteners are generally manufactured having sizes on anorder of millimeters, an obstruction of the very tiny internal socket ofa fastener may be difficult to remove.

Although resorbable fasteners are inherently not as strong as metalfasteners with regard to rigidity, sheer strength, etc., resorbablefasteners offer very important benefits for medical applications,including biocompatability and resorbability. Since resorbable materialsare relatively weak, as compared to the strength of metal, designconsiderations for resorbable fastener should maximize strength.

The specific internal-socket design of the prior art resorbable fastenerdoes not appear to be particularly suited for medical and otherapplications where the strength of the non-magnetic fastener should beoptimized. When a prior art internal-socket resorbable fastener isfirmly secured into bone, for example, the driver may in some instancesdisrupt (strip) the internal socket of the fastener. Since theinternal-socket is positioned along the rotational axis of theresorbable fastener, a very small moment arm must be utilized to rotatethe fastener, resulting in the exertion by the driver of a relativelyhigh rotational force onto the walls of the internal socket. The tinyconstruction of each internal-socket fastener (on the order ofmillimeters), the relatively weak material, and the relatively smallapplication moment arm of the internal-socket fastener, all contributeto the relative sensitivity of the system. A need has thus existed inthe prior art for a non-magnetic fastener having increased strength.

In additional to the limited strength associated with prior artnon-magnetic fasteners, prior art non-magnetic fasteners have alsosuffered from relatively thick heads. As a result of the relatively weakmaterial of the prior art internal-socket fastener, the head of theinternal-socket fastener is typically manufactured to have a relativelythick dimension in a direction parallel to the rotational axis of thefastener. The thicker head of the prior art fastener provides a greatersurface area for frictional application of torque by the driver uponinsertion of the driver into the internal socket of the fastener. Therelatively thick head of the prior art fastener, however, canundesirably protrude from the surface within which it is mounted, thuscreating an undesirable non-flush surface.

As a result of the relatively small dimensions of the resorbablefasteners in the context of, for example, bone repair and regenerationapplications, the tiny resorbable fasteners are prone to beingimproperly placed into the target structure. The prior art driver doesnot firmly hold the fastener and, accordingly, may not accurately alignthe axis of the fastener with the axis of the driver. The fastener canthus be inadvertently cross threaded or otherwise improperly securedwithin the target structure. Additionally, as a result of the relativelyloose fit between the prior art fastener and driver, the fastener maybecome dislodged from the target structure and/or the driver, beforebeing completely secured within the target structure.

Prior art drivers used to secure fasteners into target structures aretypically not disposable. Accordingly, a single driver is used to securea plurality of fasteners into the target structure or structures. Theuser is thus required to manually pick up and align each fastener withboth the target structure and the driver, before the fastener can besecured within the target structures. Additionally, due in part to therelatively tiny dimensions of the fastener, a user may accidentallyobtain a fastener, having a size other than the desired size, andattempt to secure the improperly-sized fastener into the targetstructure. The process of manipulating the fastener from the operatingtable into the target structure, accordingly, can be time consuming andsubject to human error. In medical applications, the handling of thefastener by the hand of the user and, further, the multiple uses of thedriver on a plurality of fasteners, can increase a probability ofinfection.

SUMMARY OF THE INVENTION

The high-torque fastener of the present invention includes a threadedshaft and a star-shaped head. In a preferred embodiment, the high-torquefastener comprises a resorbable or other non-magnetic material. A matingdriver snugly fits around the star-shaped head of the fastener, tothereby apply torque to the perimeter of the star-shaped head. Since thehigh-torque fastener does not incorporate an internal socket, thehigh-torque fastener of the present invention is immune from the priorart problem of the interior socket becoming obstructed with tissue orother debris.

In contrast to the prior art internal socket fastener, the high-torquefastener of the present invention harnesses a relatively large momentarm. Sufficient torque is generated, via frictional contact between thedriver the perimeter of the star-shaped head, without the introductionof excessive and potentially destructive frictional forces beingintroduced onto the star-shaped head. In other words, since thehigh-torque fastener of the present invention utilizes a relativelylarge moment arm, a relatively small rotational force can be used toapply relatively high torque to the fastener of the present invention.

The star-shaped head of the high-torque fastener provides a relativelylarge surface contact area for application of frictional rotationalforces by the driver and, further, facilitates a uniform distribution oftorque about the perimeter of the high-torque fastener of the presentinvention. The star-shaped head and the mating driver provides a systemfor applying relatively high rotational forces to the fastener tothereby firmly secure the fastener into a target structure. When removalof a resorbable, high-torque fastener is required, for example, the headof the high-torque fastener is not as susceptible to damage, compared tointernal socket fasteners. The resulting high-torque fastener and drivercombination of the present invention is more reliable and less subjectto damage, compared to prior art internal socket systems, even whenfasteners having sizes on the order of millimeters are used.

In accordance with one embodiment of the present invention, both thehead of the high-torque fastener and the driver comprise taperedsurfaces for providing a better frictional contact between thestar-shaped head and the driver, when the target structure comprises acounter sunk surface or when the high-torque fastener is counter sunk.The enhanced frictional contact from the tapered surfaces can increasethe application of torque to the star-shaped head by the driver, whenthe target structure comprises a counter sunk surface or when thehigh-torque fastener is counter sunk.

Although prior art internal socket fasteners required relatively thickheads for increasing the surface area between the internal socket andthe driver, the high-torque fasteners of the present invention can beconstructed having relatively thin heads. Since the head of thehigh-torque fastener of the present invention is less susceptible todamage by the driver, the head may be manufactured having smallerproportions. When the head and the driver are tapered, and thehigh-torque fastener is secured within a counter sunk hole of a targetstructure, for example, the profile of the fastener of the presentinvention is further reduced. Accordingly, the high-torque fastener ofthe present invention can be secured into a target structure in such away as to make the high-torque fastener less palpable to a patient.

The high-torque fastener and driver combination of the present inventionis constructed to facilitate fast and easy centering of the fastener onthe driver. The surface of the head of the high-torque fastener of thepresent invention is slightly rounded, and the edge forming the openingof the driver has a slight taper corresponding in radius to that of thesurface of the head of the high-torque fastener. This centering featureof the present invention can attenuate the occurrence of improperloading of the high-torque fastener within the driver.

In accordance with another aspect of the present invention, thehigh-torque fastener and the driver are configured to snugly fittogether. When the high-torque fastener is secured within the driver,any shaking of the driver by the hand of a user cannot dislodge thehigh-torque fastener therefrom. When the high-torque fastener is securedwithin the driver, a user can grip only the high-torque fastener androtate the high-torque fastener without touching the driver, so that thedriver is completely below the high-torque fastener, without thehigh-torque fastener becoming dislodged from the driver. During therotating action, the driver does not contact any object except for thehigh-torque fastener. In accordance with yet another aspect of thepresent invention, the high-torque fastener snaps into the driver tothereby provide a firm and secure fit. The strong hold of the driver onthe high-torque fastener helps to ensure proper alignment of therotational axes of the fastener and driver and, further, prevents thehigh-torque fastener from inadvertently being dislodged.

An automatic ejection mechanism is provided in accordance with yetanother aspect of the present invention, for partially ejecting thehigh-torque fastener from the driver, as the high-torque fastener issecured within a target structure or structures, to thereby facilitateremoval of the driver from around the high-torque fastener after thehigh-torque fastener is secured within the target structure orstructures.

In accordance with still another aspect of the present invention, thedriver is supplied with a high-torque fastener pre-secured therein, andis disposable. The tedious prior art process of selecting aproperly-sized fastener, orienting the fastener, and subsequentlyassisting in the alignment of the fastener between the target structureand the driver as the driver is used to rotate the fastener, is reducedor eliminated. Time is saved, resulting in saved costs in the operatingroom, for example. Additionally, potential errors from the selection ofthe wrong-sized fastener, or an inappropriate alignment of the fastenerrelative to either of the target structure or the driver, can be reducedor eliminated. The disposable driver and fastener combination of thepresent invention offers added convenience and reliability. Moreover,since a user does not have to directly handle the fastener and since thedisposable driver is only used once, any likelihood of infection can beattenuated. In accordance with yet another aspect of the presentinvention, the disposable driver and fastener combination is sold in asterilized package.

The present invention, together with additional features and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying illustrativedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a driver and fastener combination inaccordance with a first presently preferred embodiment;

FIG. 2 is a side elevation view of a fastener in accordance with thefirst presently preferred embodiment;

FIG. 3 is a side elevation view of a driver and fastener combination inaccordance with the present invention;

FIG. 4 is a top planar view of a fastener in accordance with the firstpresently preferred embodiment;

FIG. 5 is a bottom planar view of a driver in accordance with the firstpresently preferred embodiment;

FIG. 6 is a cross-sectional view of a fastener and driver combination inaccordance with the first presently preferred embodiment;

FIG. 7 is a side-elevation view of a fastener and driver combinationwherein the fastener is partially inserted into two members, inaccordance with the first presently preferred embodiment;

FIG. 8 is a cross-sectional view of a fastener and driver combinationwherein the fastener is fully inserted into the two members, inaccordance with the first presently preferred embodiment;

FIG. 9 is a side-elevation view of a fastener and driver combination inaccordance with the first presently preferred embodiment;

FIG. 10 is a top planar view of a fastener in accordance with a secondpresently preferred embodiment;

FIG. 11 is a bottom planar view of a driver in accordance with thesecond presently preferred embodiment;

FIG. 12 is a cross-sectional view of a driver in accordance with thesecond presently preferred embodiment;

FIG. 13 is a side-elevation view of a fastener in accordance with thesecond presently preferred embodiment;

FIG. 14 is a top planar view of a fastener in accordance with anotherembodiment of the presently preferred invention;

FIG. 15 is a cross-sectional view of a fastener and driver combinationwherein the fastener is partially secured into a target structure, inaccordance with a third presently preferred embodiment; and

FIG. 16 is a cross-sectional view of a fastener and driver combinationwherein the fastener is fully inserted into the target structure, inaccordance with the third presently preferred embodiment.

FIG. 17A-17C are schematic illustrations of buttress-style threads inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to the drawings, FIG. 1 illustrates afastener and driver assembly 20 comprising a driver 22 and a high-torquefastener 24. The high-torque fastener 24 comprises a threaded shaft 26having a shaft proximal end 28, a shaft distal end 31, and a shaftrotational axis 33 extending therebetween. A shaft diameter 36 (FIG. 2)is measured in a direction transverse to the shaft rotational axis 33.

The high-torque fastener 24 further comprises a head 40 which isconnected to the shaft proximal end 28. As best seen in FIG. 2, the head40 comprises a head proximal end 45, a head distal end 47, and a headrotational axis 49. A head diameter 51 is measured in a directiontransverse to the head rotational axis 49, and a head perimeter 55 isdefined as a surface of the head 40 surrounding a perimeter of the head40.

The driver 22 comprises a driver opening 61 which is defined by anopening perimeter surface 63. As best seen in FIG. 3, the driver 22comprises a driver proximal end 66, a driver distal end 68, and a driverrational axis 70 extending between the driver proximal end 66 and thedriver distal end 68. The driver opening 61 is disposed within thedriver 22 at the driver distal end 68 and is adapted for accommodatingthe head 40 of the high-torque fastener 24 therein.

As shown in FIGS. 1 and 2, the head proximal end 45 comprises a firstcurved surface 73 which has a substantially constant first radius ofcurvature and which is symmetrical about the head rotational axis 49.Referring particularly to FIG. 2, the first curved surface 73 can beexpressed as follows. A first distance measured from a first point 81 onthe first curved surface 73 near the head rotational axis 49 to a thirdpoint 84 on the shaft distal end 31, is greater than a second distancemeasured from a second point 86 near the head perimeter 55 on the firstcurved surface 73 to the third point 84 on the shaft distal end 31.

Turning back to FIG. 1, the second curved surfaces 90 are disposedadjacent to the opening perimeter surface 63 to contact the first curvedsurface 73, when the head 40 is placed into contact with the secondcurved surfaces 90 in a rotationally misaligned manner. The phantom line93 in FIG. 9 is drawn tangent to two of the second curved surfaces 90and, further, is drawn to intersect the driver rotational axis 70. Inthe presently preferred embodiment, a radius of curvature of the phantomline 93 is approximately equal to a radius of curvature of the firstcurved surface 73. A user placing the first curved surface 43 intocontact with the second curved surfaces 90 of the opening perimetersurface 63, in a rotationally-misaligned orientation so that the head 40does not fit into the driver opening 61, will experience aself-centering effect resulting from the first curved surface 73 of thehead 40 and the second curved surfaces 90 of the opening perimeter 63.The self-centering effect tends to maintain an alignment of the shaftrotational axis 33 with the driver rotational axis 70, as the userrotates the high-torque fastener 24 about the shaft rotational axis 33in an attempt to facilitate a proper fit of the head 40 within thedriver opening 61. This self-centering feature of the present inventionfacilitates relatively easy loading of the high-torque fastener 24 intothe driver 22.

Referring now to FIG. 4, the head 40 of the high-torque fastener 24preferably comprises a plurality of radially-extending protrusions 96spaced along the head perimeter 55. The radially-extending protrusions96 are preferably evenly spaced along the head perimeter 55. The pointof each radially extending protrusion 96 is preferably disposed amaximum radial distance away from the head rotational axis 49. Theplurality of radially-extending protrusions 96 preferably form a starshape having six slightly-rounded points 96.

FIG. 5 is a bottom planar view of the driver 22, illustrating how theopening perimeter surface 63 very closely corresponds to the headperimeter 55 (FIG. 4), to thereby insure a snug fit between the two.

Although six radially-extending protrusions 96 are presently preferred,other numbers of points may be used in other modified embodiments. Inthe presently preferred embodiment, wherein relatively weak materialsare used for the high-torque fastener 24, as compared to metal, andwherein the high-torque fastener 24 is manufactured to have a relativelysmall size on the order of millimeters, a maximum of six to eight pointson the head 40 is preferred for maximum surface area, strength, andoperability. In other embodiments, as few as 3 points and as many as 12points may be used. In still other modified embodiments, fewer orsubstantially greater (20 or more) numbers of points may be used.

FIG. 10 illustrates a top planar view of a high-torque fastener 124 inaccordance with a second preferred embodiment of the present invention,and FIG. 14 illustrates a top planar view of a high-torque fastener 224in accordance with another modified embodiment of the present inventioncomprising only four points. Regardless of the particular configurationof the head of the high-torque fastener, the driver of the presentinvention is preferably precisely manufactured to snugly fit around thehead perimeter of the high-torque fastener. In other non-interchangeableembodiments in connection with the use of other materials, for example,other numbers of points on the star-shaped head and other complimentarystar-shaped driver openings may be used. Additionally, in other modifiedembodiments, the star shape may be changed to provide other shapes, suchas a fluted, corrugated, or ribbed configurations. The star shape of thepresent invention provides for a greater surface area and, consequently,a better friction grip and larger distribution of the applied torqueforces between the head of the high-torque fastener 24 and the openingperimeter surface 63 of the driver 22, as compared to the surface areaof a conventional hex-head bolt, for example.

In accordance with the present invention, rotational forces arefrictionally applied by the driver 22 to the head perimeter 55, tothereby distribute rotational forces around the head 40 of thehigh-torque fastener 24. As a result of the large moment arm, thestrength of the high-torque fastener 24 is limited only by the inherentsheer strength of its material.

In a presently preferred embodiment, high-torque fasteners 24 are usedto secure plates to bone for skeletal repair. High-torque fasteners 24can also be used to secure sheets, meshes, and other membrane barriers,for example, to bone for skeletal repair. Co-pending U.S. applicationSer. No. 08/699,673, filed on Aug. 19, 1996 and commonly assigned,discloses such membranes.

The high-torque fasteners 24, when used for skeletal repair or othersurgical applications, are preferably relatively small in size. Aspresently embodied, the high-torque fasteners 24 are formed with shaftdiameters 36 of 2 mm or 2.5 mm, and corresponding head diameters 51 of3.7 mm. In another preferred embodiment, the high-torque fasteners 24are formed having shaft diameters 36 of approximately 1.5 mm and headdiameters 51 of approximately 2.8 mm. In modified embodiments, thehigh-torque fasteners 24 are formed with shaft diameters 36 from about 1mm to about 5 mm.

The high-torque fasteners 24 preferably comprise non-magnetic materials.In skeletal repair applications, for example, the high-torque fasteners24 preferably comprise resorbable materials and, to date, preferablycomprise polymers and/or co-polymers made from lactic acid and/orglycolic acid. Other materials such as other resorbable ornon-resorbable materials, including biocompatible materials, may also beused. The head diameters and other dimensions, including thread size,head design, shaft diameter, etc., may be made smaller, larger, orotherwise modified or changed depending on the particular application inaccordance with other modified embodiments of the present invention. Inaddition to the above-mentioned shaft and head diameters, the relativedimensions depicted in FIGS. 1-16 are specifically contemplated by thepresent inventors.

FIG. 6 illustrates a cross-sectional view of the high-torque fastener 24firmly secured within the driver 22. The first curved surface 73 isinserted into the driver opening 61 until the first curved surface 73contacts an interior surface of the driver 22. In accordance with oneembodiment, the contacting of the first curved surface 73 with aninterior surface of the driver 22 results in a snap fit.

The snap fit is achieved, for example, when relatively large insertionforces are applied to move the high-torque fastener 24 into the driver22. The relatively large insertion forces are initially met withfrictional counter forces, resulting in a relatively slow movement ofthe high-torque fastener 24 into the driver 22 as insertion forces aremaintained. The relatively large insertion forces, at an intermediatepoint in the insertion process, are met with somewhat reduced frictionalforces, resulting in an acceleration of the high-torque fastener 24. Thehigh-torque fastener 24 then travels a small distance until the firstcurved surface 73 contacts the interior surface of the driver 22 andthen rapidly decelerates. The contacting of the first curved surface 73with the interior surface of the driver 22 results in the snap fit,which provides a verification to the user that the high-torque fastenerhas been fully and properly seated within the driver 22. Theverification of the snap fit can comprise an audible snap soundindicating that the high-torque fastener cannot be inserted further intothe driver 22.

When the high-torque fastener 24 is firmly secured within the driver 22,the head perimeter 55 of the high-torque fastener 24 is frictionallyengaged with the opening perimeter surface 63. The tapered portion 103of the driver 22 tapers in a distal direction, from an area between thedriver proximal end 66 and the driver distal end 68, decreasing indiameter to the driver distal end 68. The tapered portion 101 of thehead 40 tapers in a distal direction from the head perimeter 55 to theshaft proximal end 28. In the presently preferred embodiment, thetapered portion 101 of the high-torque fastener 24 has a slope which isapproximately equal to the tapered portion 103 of the driver 22. In apreferred embodiment, the slope forms an angle of 45 degrees with theshaft rotational axis 33 of the high-torque fastener 24.

FIG. 7 shows that the tapered portion 101 of the head 40 is not flushwith the tapered portion 103 of the driver 22 when the high-torquefastener 24 is fully secured within the driver 22. FIG. 8 shows how thetapered portion 103 of the driver 22 is substantially flush with thetapered portion 101 of the head 40 when the high-torque fastener 24 iscompletely secured into a target structure or structures. Rotation ofthe driver 22 in the direction of the arrow A1 threads the high-torquefastener 24 through a first object 111 and into a second object 113,such as bone. As shown in FIG. 7, a countersunk aperture 116 ispreferably formed within each aperture of the first object 111.

The high-torque fastener 24 can be firmly secured within the firstobject 111 and the second object 113 by a user rotating the driver 22 inthe direction of the arrow A1, as illustrated in FIG. 8. As thehigh-torque fastener 24 is fully secured into the first object 111 andthe second object 113, the high-torque fastener 24 is partiallyself-extracted out of the driver opening 61 of the driver 22. FIG. 8shows how the self-extraction partially removes the first curved surface73 from contact with a portion of the driver 22. A relatively largeamount of force is required to remove the driver 22 from the head 40,when the high-torque fastener 24 is fully seated within the driver 22,as illustrated in FIGS. 6 and 7, for example. After the high-torquefastener 24 is partially self-extracted as shown in FIG. 8, however, thedriver 22 can be removed from around the head perimeter 55 of thehigh-torque fastener 24, with substantially less effort.

In accordance with a preferred embodiment of the present invention, theradius of curvature of the first curved surface 73 provides a varyingthickness across the diameter of the head 40 while still reducing apalpability of the high-torque fastener 24 to a patient. Thicknesses ofthe head 40 vary with distance from the head rotational axis 33, so thatportions of the head 40 closer to the head rotational axis 33 arethicker than portions further from the head rotational axis 33. Portionsof the head 40 between the radially extending protrusions 196 arethicker than portions on the radially extending protrusions 196, as aresult of the varying thickness across the diameter of the head 40. Thethicker portions of the head 40 between the radially extendingprotrusions 196 help to provide a firm grip of the driver 22 about thehigh-torque fastener 24, especially when the high-torque fastener 24 isfully seated or almost fully seated. When the high-torque fastener 24 isfully seated or almost fully seated within, for example, the firstobject 111 and the second object 113, and is being either secured orremoved, the thicker inner portions of the head 40 between the radiallyextending protrusions 196 enhance the strength of the head 40 andenhance the grip of the driver 22 about the head 40.

After the high-torque fastener 24 is fully secured into the first object111 and second object 113, the driver 22 can be removed. The driver 22can subsequently be placed back around the head perimeter 55 of thehigh-torque fastener 24, to thereby facilitate removal of thehigh-torque fastener 24. After placing the opening perimeter surface 63of the driver 22 over the head perimeter 55 of the high-torque fastener24, a user can rotate the driver 22 in a direction opposite to the arrowA1, to thereby rotate the high-torque fastener 24 out of the firstobject 111 and the second object 113.

Rotation of the high-torque fastener 24 in a direction opposite to thearrow A1 results in movement of the high-torque fastener 24 in adirection toward the driver 22. After the high-torque fastener 24 hasmoved a predetermined distance in a direction from the first object 111and the second object 113 toward the driver 22, the driver 22 can bepushed distally toward the first object 111 and the second object 113,to thereby fully and firmly seat the head 40 of the high-torque fastener24 within the driver opening 61. When the head 40 is fully seated withinthe driver opening 61, the first curved surface 73 of the high-torquefastener 24 contacts an inner portion of the driver 22. This contactingresults in a snap fit in accordance with one embodiment of the presentinvention. Accordingly, when the high-torque fastener 24 is insertedinto the countersunk aperture 116, the countersunk aperture 116 forcesthe driver 22 off of the high-torque fastener 24 to some extent so thatthe driver 22 can be removed from the head 40 with relative ease whenthe high-torque fastener 24 is fully secured within the first object 111and the second object 113.

The tapered portion 103 of the driver 22 is substantially flush with thetapered portion 101 of the high-torque fastener 24, when the high-torquefastener 24 is firmly secured within the first object 111 and the secondobject 113. The countersunk aperture 116 as presently embodied helps toflush mount the head 40 of the high-torque fastener 24 to the firstobject 111. The tapered portion 103 of the driver 22 is adapted to fitwithin the countersunk aperture 116 to thereby allow the openingperimeter surface 63 of the driver 22 to reach a maximum distance withinthe countersunk aperture 116 and fit around the head perimeter 55.Again, as the high-torque fastener 24 is removed from the first object111 and the second object 113, the driver 22 can be pushed further ontothe head 40 of the high-torque fastener 24, to thereby fully seat thehigh-torque fastener 24 within the driver 22.

In accordance with the present invention, a removal force required toremove the driver 22 from the head 40 in the fully seated position isgreater than a removal force required to remove the driver 22 from thehead 40 in the self-extracted position. As presently preferred, theremoval force required to remove the driver 22 from the head 40 in thefully seated position is at least 10 percent and, more preferably atleast 20 percent, greater than the removal force required to remove thedriver 22 from the the head 40 in the self-extracted position. Even morepreferably, the removable force for the fully seated position is twiceand, more preferably ten times, as large as the removable force for theself-extracted position. Greater removal forces may be configured inmodified embodiments. When the tapered portion 103 of the high-torquefastener 24 is fully within the countersunk aperture 116, a proximalportion 121 (FIG. 6) extends above the surface of the countersunkaperture 116, to facilitate gripping thereof by the opening perimetersurface 63 of the driver 22.

FIGS. 10-13 illustrate a second presently preferred embodiment of ahigh-torque fastener and driver combination, wherein like numbers aredesignated with like numerals precoded by a “1”. The head 140 of thehigh-torque fastener 124 comprises a plurality of radially extendingprotrusions 196. A threaded shaft 126 is connected to the head 140.FIGS. 11 and 12 illustrate bottom planar and cross-sectional views ofthe driver 122, which comprises a driver distal end 168 having anopening perimeter surface 163 therein. The high-torque fastener 124comprises a tapered portion 1101, as illustrated in FIG. 13.

Operation of the driver 122 and the high-torque fastener 124 is verysimilar to that of the high-torque fastener 24 and driver 22 discussedabove. In a presently preferred embodiment, the driver 122 isconstructed in a form similar to the driver 22, having a tapered portionparallel to the tapered portion 1101 of the high-torque fastener 124. Inan embodiment where the driver 122 comprises a tapered portion, thehigh-torque fastener 124 is adapted to be secured into a countersunkhole so that the top surface of the high-torque fastener 124 is flushwith a surface of the first object. In other embodiments, thehigh-torque fastener 124 comprises a first curved surface similar to thefirst curved surface 73 of the high-torque fastener 24, and the driver122 comprise second curved surfaces similar to the second curvedsurfaces 90 of the driver 22.

FIG. 14 illustrates an embodiment of a high-torque fastener 224, whereinonly four radially extending protrusions 296 are disposed about the head240. FIGS. 15 and 16 illustrate a third preferred embodiment of thepresent invention, wherein like elements are designated with likenumerals preceded by a “3”. The driver 322 comprises tapered portions3103 for contacting surfaces of a countersunk aperture 3116 of a firstobject 3111. In FIG. 15, a first curved surface 373 of the high-torquefastener 324 abuts against an inner surface of the driver 322. A headperimeter 355 contacts an opening perimeter surface 363 of the driver322. The star or corrugated shape of the head 340 of the high-torquefastener 324 increases the surface of the driven area of the high-torquefastener 324 and allows the torque to be distributed and applieduniformly to the high-torque fastener 324. This structure when used in acountersunk aperture 3116 allows for a shallower head 340, relative tothe prior art, which is critical to certain applications, such as, theuse in surgery wherein the total thickness is important since thehigh-torque fastener 324 should not be palpable to the patient. FIG. 16shows the high-torque fastener 324 in a self-extracted position,relative to the driver 322, wherein the first curved surface 373 of thehigh-torque fastener 324 is substantially flush with the surface of thefirst object 3111.

Since the depth of the driver opening 361 is greater than a height ofthe head 340, the driver 322 can be seated on the first object 3111before the high-torque fastener 324 is fully seated, as shown in FIG.15. By continuing to tighten the high-torque fastener 324, thehigh-torque fastener 324 is pulled from the driver 322, as shown in FIG.16. The driver 322 may subsequently be removed from the head 340 withrelative ease.

The tapered portion 3103 of the driver 322 is adapted to fit within thecountersunk aperture 3116, even when the high-torque fastener 324 isfully seated therein, as shown in FIG. 16. If removal of the high-torquefastener 324 from the first object 3111 is required, there is moresurface area on head 340 for the driver 322 to contact due to thecountersunk-oriented structure. The removal of the high-torque fastener324 is thus possible and easier, relative to the prior art, with lesschance for damage to the head 340 of the high-torque fastener 324. Uponrotation of the driver 322 in a countersunk direction, the high-torquefastener 324 can be slightly removed from the countersunk aperture 3111,as illustrated in FIG. 15. As further shown in FIG. 15, after thehigh-torque fastener 324 is slightly removed from the countersunkaperture 311, the driver 322 can be pushed further over the high-torquefastener 324 to thereby firmly grip and fully seat the high-torquefastener 324 therein, thus facilitating centering of a rotational axisof the high-torque fastener 324 with a rotational axis of the driver322.

The present inventors have discovered a number of unique ratios withregard to the configuration of the inventive high-torque fasteners. Inaccordance with the present invention, the ratio of the inner headdiameter to the maximum head diameter should preferably be about 0.9 orless and, more preferably, should be about 0.7 or less. In FIG. 4, aratio of an inner head diameter 41 to a maximum head diameter of thehead 40 is approximately 0.71. In FIG. 10, a ratio of an inner headdiameter 141 to a maximum head diameter 142 of the head 140 isapproximately 0.69. FIG. 14 illustrates a head 240, wherein a ratio ofan inner head diameter 241 to a maximum head diameter 242 isapproximately 0.61. In the configuration of FIG. 13, a ratio of an innerhead diameter 140 a to a maximum head diameter 140 b of the head 140 isapproximately 0.57.

In accordance with the present invention, a ratio of a minimum diameterof the opening perimeter surface 63 of the driver 22 to maximum diametera of the opening perimeter surface 63 of the driver 22 is approximately0.71, as can be seen from FIG. 5. A ratio of a minimum diameter 164 ofthe opening perimeter surface 163 of the driver 22 to a maximum diameter166 of the opening perimeter surface 163 of the driver 22 isapproximately 0.69, as can be seen from FIG. 11.

A ratio of the shaft diameter to the inner head diameter is about 0.9and, more preferably, is about 0.7. For example, as shown in FIG. 2, aratio of the shaft diameter 36 to the inner head diameter is about 0.6.

In accordance with another embodiment of the present invention, a ratioof a maximum head thickness to a maximum head diameter is about 0.4, anda ratio of a maximum head thickness to the shaft diameter is about 0.8.For example, in FIG. 13 a ratio of a maximum head thickness 143 a to themaximum head diameter 140 b is about 0.44. Similarly, in FIG. 13, aratio of the maximum head thickness 143 a to the shaft diameter 140 a isabout 0.77.

As shown in FIG. 6, a height 102 of a proximal non-tapered portion to atotal height 104 of the head 40 is about 0.51. As can be seen from FIG.13, a ratio of a minimum head thickness 142 to a maximum head thickness143 a is about 59 percent. Especially in the context of resorbablehigh-torque fasteners for medical use, it is preferred to have arelatively high fastener-head to shaft ratio for the benefit offacilitating greater application of torque onto the fastener. Such aratio may also facilitate a smaller fastener head thickness, which canrender the fastener less palpable to the patient. Smaller diametershafts can yield greater probabilities of the shaft sheering.

Turning now to FIGS. 17A-17C, the threads of the present inventionpreferably comprise buttress-style threads which are uneven on opposingsides thereof. As one example, the spiral ribs which encircle the shaftof the high-torque fastener and which define the thread, comprise oneside which is zero degrees relative to a perpendicular line and anotherside which is 45 degrees relative to a perpendicular line, as shown inFIG. 12A. The perpendicular line is measured relative to an axis of thehigh-torque fastener. In the presently preferred embodiment, the 45degree angle side of the rib defining the thread is on the leading sideof the high-torque fastener, which is opposite to the head side of thehigh-torque fastener. In the presently preferred embodiment, as shown inFIG. 12B, the spiral ribs which encircle the shaft of the high-torquefastener and which define the thread, comprise one side which is sevendegrees relative to a perpendicular line and another side which is 45degrees relative to a perpendicular line. In an embodiment as shown inFIG. 12C, the spiral ribs which encircle the shaft of the high-torquefastener and which define the thread, comprise one side which is fivedegrees relative to a perpendicular line and another side which is 45degrees relative to a perpendicular line, as shown in FIG. 12A. Thesharp leading angle allows for easier (low torque) insertion and theflatter following angle requires greater (high torque) removal forces.The buttress-style threads can be configured in various shapes and sizesin modified embodiments.

In a preferred embodiment the driver and high-torque fastener arepackaged as a unit in which the high-torque fastener is fully seatedwithin the driver. In surgery, for instance, this feature eliminates theneed for the nurse or surgeon to load the high-torque fastener into thedriver, saving operating-room time and costs and, further, increasingconvenience and reliability. Due in part to the extremely small size ofthe resorbable fasteners in general, the systems can be difficult toassemble in practice. The pre-assembled unit using a disposable driverin accordance with the present invention eliminates this problem.

The driver is color coded to indicate the size of the high-torquefastener to which the driver is attached, in accordance with oneembodiment of the present invention. For example, the driver comprises ablue color to indicate that the attached high-torque fastener has ashaft diameter of 2 mm, and the driver comprises a color of red toindicate that the attached high-torque fastener has a shaft diameter of1.5 mm. The color coding of the driver, in combination with thepre-attachment of the appropriately-sized high-torque fastener, canattenuate or eliminate any error of using an unintended high-torquefastener size. The high-torque fasteners may be color coded to indicatehigh-torque fastener size in addition to, or as an alternative to, colorcoding of the driver. This color coding of the high-torque fasteners,however, may add an undesirable or potentially hazardous substance forthe patient to the resorbable implant. The high-torque fastenerspreferably are resorbable and, to date, preferably comprise polymersand/or co-polymers made from lactic acid and/or glycolic acid. Othermaterials, such as other resorbable or non-resorbable materials,including bio-compatible materials, may be used in other embodiments.

The high-torque fastener and driver system of the present invention hasparticular applicability in a context of (1) providing efficient meansof removably attaching a high-torque fastener to a driver and (2)providing added strength and operability to non-magnetic high-torquefasteners and fastening means. In other embodiments of the invention,the high-torque fasteners can comprise other non-magnetic materials,such as plastic, wood, resin, recyclable substances, etc. The termnon-magnetic is used herein to refer to materials low in steel and iron,and other materials that do not significantly interact with magnets.Although the prior art has used magnets to attach metallic (containingsteel or iron) fasteners to drivers, magnets would not work fornon-magnetic high-torque fasteners, including titanium, aluminum, brassand/or stainless-steel fasteners.

Although the high-torque fastener and driver system of the presentinvention has been described in the context of medical applications, thesystem of the present invention can be used in a wide variety of otherapplications. For example, high-torque fasteners made of wood may beused with furniture. Additionally, recyclable high-torque fasteners maybe used for securing recyclable products together.

The structure of the present invention, which facilitates a very snugfit of a high-torque fastener head to a driver, can be used with metal(including iron and steel) high-torque fasteners for conventionalapplications, as well. For example, a user may desire to inset a metalhigh-torque fastener into a blind area, such as a deep recess, where thehigh-torque fastener needs to be gripped by the driver and securelyheld. The high-torque fastener may need to be securely held for a givendistance under vibrational or other turbulent conditions, for example.

According to the presently preferred embodiment, in the context of metalhigh-torque fasteners, for example, the high-torque fastener head andthe driver configuration are precisely manufactured to ensure a snug fitbetween the two. The snug fit allows for the driver to securely andfrictionally hold the head of the high-torque fastener. When additionalfrictional holding of the high-torque fastener by the driver isrequired, the thickness of the head, measured along an axis of thehigh-torque fastener, can be increased to thereby increase thesurface-contacting area between the driver and the head of thehigh-torque fastener.

Although an exemplary embodiment of the invention has been shown anddescribed, many other changes, modifications and substitutions, inaddition to those set forth in the above paragraphs, may be made by onehaving ordinary skill in the art without necessarily departing from thespirit and scope of this invention.

What is claimed is:
 1. A fastener and driver assembly, comprising: (a) a resorbable fastener including: (i) a threaded shaft having a shaft proximal end, a shaft distal end, and a shaft rotational axis extending therebetween, the threaded shaft having a shaft diameter measured in a direction transverse to the shaft rotational axis; (ii) a head connected to the shaft proximal end, the head having a head proximal end, a head distal end, and a head rotational axis extending therebetween, the head having a head diameter measured in a direction transverse to the head rotational axis and a head perimeter; and (b) a driver having a driver proximal end, a driver distal end and a driver rotational axis extending therebetween, the driver having a driver opening at the driver distal end for accommodating the head therein; (c) wherein the head proximal end comprises a first curved surface which has a substantially constant first radius of curvature and which is symmetrical about the head rotational axis, a first distance being measured from a first point on the first curved surface near the head rotational axis to the shaft distal end, a second distance being measured from a second point near the head perimeter on the curved surface to the shaft distal end, the first distance being greater than the second distance; and (d) wherein the driver distal end comprises an opening perimeter surface which defines the driver opening in the driver distal end, the opening perimeter surface comprising a second curved surface which has a substantially constant second radius of curvature that is substantially equal to the first radius of curvature.
 2. The fastener and driver assembly as set forth in claim 1, wherein: (a) the head perimeter of the fastener forms a star shape (b) the opening perimeter surface of the driver end forms a star-shaped opening which generally corresponds in size and configuration to the star shape formed by the head perimeter of the fastener.
 3. A fastener and driver assembly, comprising: (a) a resorbable fastener including: (i) a threaded shaft having a shaft proximal end, a shaft distal end, a shaft rotational axis extending therebetween, the threaded shaft having a shaft diameter measured in a direction transverse to the shaft rotational axis; and (ii) a head connected to the shaft proximal end, the head having a head proximal end, a head distal end, and a head rotational axis extending therebetween, the head having a head diameter measured in a direction transverse to the head rotational axis and a head perimeter, the head distal end comprising a tapered portion having a first slope; and (b) a driver having a driver proximal end, a driver distal end and a driver rotational axis extending therebetween, the driver further having a driver opening at the driver distal end for accommodating the head therein, the driver distal end comprising a tapered portion having a second slope; (c) wherein the first slope is substantially equal to the second slope when the head is secured within the driver opening.
 4. The fastener and driver assembly as set forth in claim 3, wherein: the tapered portion of the head distal end tapers in a distal direction, the tapered portion of the head distal end beginning near the head perimeter and decreasing in diameter to the shaft proximal end; and the tapered portion of the driver distal end tapers in a distal direction, the tapered portion of the driver distal end beginning in an area between the driver proximal end and the driver distal end, and decreasing in diameter to the driver distal end.
 5. The fastener and driver assembly as set forth in claim 4, wherein: the head of the fastener is adapted to snugly fit within the driver opening when the driver distal end accommodates the head therein; and the tapered portion of the head distal end is substantially flush with the tapered portion of the driver distal end when the driver distal end accommodates the head therein.
 6. The fastener and driver assembly as set forth in claim 4, wherein: the head of the fastener is adapted to snugly fit within the driver opening when the driver distal end accommodates the head therein; the tapered portion of the head distal end is not substantially flush with the tapered portion of the driver distal end when the driver distal end has fully accommodated the head therein but not yet fully secured the fastener into a target; and the tapered portion of the head distal end is not substantially flush with the tapered portion of the driver distal end when the driver distal end has been, first, placed over and around a head of a fastener which was previously secured into a target and, then, rotated to partially remove the fastener from the target and, finally, pushed in a distal direction further over and around the fastener.
 7. The fastener and driver assembly as set forth in claim 4, wherein: the head of the fastener is adapted to snugly fit within the driver opening when the driver distal end accommodates the head therein; the tapered portion of the head distal end is substantially flush with the tapered portion of the driver distal end when the driver distal end has, after first accommodating the head therein, secured the fastener into a target; and the tapered portion of the head distal end is substantially flush with the tapered portion of the driver distal end when the driver distal end is placed over and around a head of a fastener, which has been previously secured into a target.
 8. A fastener and driver assembly, comprising: (a) a resorbable fastener including: (i) a threaded shaft having a shaft proximal end, a shaft distal end, and a shaft rotational axis extending therebetween, the threaded shaft having a shaft diameter measured in a direction transverse to the rotational axis; and (ii) a star-shaped head connected to the proximal end of the threaded shaft, the star-shaped head having a head proximal end, a head distal end, and a head rotational axis extending therebetween, the star-shaped head having a head diameter measured in a direction transverse to the head rotational axis and a star-shaped head perimeter; and (b) a driver having a driver proximal end, a driver distal end and a driver rotational axis extending therebetween, the driver further having a star-shaped driver opening at the driver distal end for accommodating the head therein. 